1. Field of the Invention
The present invention relates to a honeycomb structure and an exhaust gas treatment apparatus.
2. Description of the Related Art
Conventionally, honeycomb structures are employed in exhaust gas treatment apparatuses used for treating NOx and the like in exhaust gases of automobiles (e.g. WO2005/063653A1).
Basic framework parts such as cell walls of a honeycomb structure are made of alumina, for instance. On the cell walls, a noble metal catalyst such as platinum, for example, and a NOx storage catalyst including an alkali metal salt, an alkaline earth metal salt or the like, are supported. Generally, in the case where the exhaust gas is an oxidizing atmosphere (for example, during normal operation of a diesel engine), the noble metal catalyst plays a role in oxidizing NOx (such as NO and NO2) in the exhaust gas to NO3 when the exhaust gas passes into the honeycomb structure. On the other hand, the NOx storage catalyst temporarily adsorbs NO3 produced in this oxidation reaction. NO3 adsorbed by the NOx storage catalyst is, when the exhaust gas is switched to a reducing atmosphere (for example, during rich spike control of the diesel engine), reduced to N2 via the noble metal catalyst and then discharged out of the honeycomb structure system.
Accordingly, NOx in the exhaust gases of an automobile can be treated by passing the exhaust gases into a honeycomb structure having such a configuration.
The contents of WO2005/063653A1 are incorporated herein by reference.